The CPI measures price changes in a basket of goods and is used to measure price inflation. As of the end of August, the CPI gained 1.5% since August 2012.

People who buy groceries or go to the doctor scoff at the CPI, because it doesn't reflect their experience at the store or the clinic. But it's not meant to: It's supposed to give a broad overview of prices. So it includes changes in the price of gasoline (down 2.4% the past 12 months) to chicken (up 6.5%) to rent (up 3%).

There are lots of ways to criticize the CPI. For example, the CPI's basket of goods is based on surveys about what people buy. Your expenses may vary, particularly if you have a long commute or children in college.

The CPI is no longer the only game in town, but most measures follow the CPI fairly closely. The Billion Prices Project at the Massachusetts Institute of Technology samples prices on the Internet. It has risen a bit less than 2% the past 12 months. The Everyday Price Index, created by the American Institute for Economic Research, has risen 1.52% the past 12 months.

However you measure it, inflation is the enemy of investors: 10 years of 1.5% inflation will reduce your buying power by 14%. Your aim should be to get returns that, at the very least, beat inflation. Right now, CDs or money funds won't do that.